In reference to humans, as a condition of certain skin diseases, it is attested from c.1400. As what falls from one's eye when blindness ends (usually figurative), it echoes Acts ix:18 (Latin tanquam squamæ, Greek hosei lepides).

The connecting sense seems to be of half of a bivalve ("split") shell used as a drinking cup or a pan for weighing. But according to Paulus Diaconus the "drinking cup" sense originated from a supposed custom of making goblets from skulls (see skull). Related: Scales. This, as a name for the zodiac constellation Libra, is attested in English from 1630s.

scale

v.1

"to climb by or as by a ladder," late 14c., from scale (n.) "a ladder," from Latin scala "ladder, flight of stairs," from *scansla, from stem of scandere "to climb" (see scan (v.)). Related: Scaled; scaling.

scale

scale

v.3

"weigh in scales," 1690s, from scale (n.2). Earlier "to compare, estimate" (c.1600). Meaning "measure or regulate by a scale" is from 1798, from scale (n.3); that of "weigh out in proper quantities" is from 1841. Scale down "reduce proportionately" is attested from 1887. Scale factor is from 1948. Related: Scaled; scaling.

scale

n.3

"series of registering marks to measure by; marks laid down to determine distance along a line," late 14c., from Latin scala "ladder, staircase" (see scale (v.1)). Meaning "succession or series of steps" is from c.1600; that of "standard for estimation" (large scale, small scale, etc.) is from 1620s. Musical sense (1590s), and the meaning "proportion of a representation to the actual object" (1660s) are via Italian scala, from Latin scala.

One of the small thin plates forming the outer covering of fish, reptiles, and certain other animals.

A similar part, such as one of the minute structures overlapping to form the covering on the wings of butterflies and moths.

A small, thin, usually dry plant part, such as one of the protective leaves that cover a tree bud or one of the structures that contain the reproductive organs on the cones of a conifer.

A plant disease caused by scale insects.

scale 2

(skāl)

An ordered system of numbering or indexing that is used as a reference standard in measurement, in which each number corresponds to some physical quantity. Some scales, such as temperature scales, have equal intervals; other scales, such as the Richter scale, are arranged as a geometric progression.